Then last month Kelly was charged with Blagojevich in a sweeping indictment accusing him of being part of a criminal enterprise that saw Blagojevich's powers as governor leveraged in exchange for campaign contributions. A conviction on all three cases could add up to significant prison time.

As previously reported, three of the former governor's former chiefs of staff -- John Wyma, Alonzo "Lon" Monk and John Harris -- are expected to be witnesses against him.

Antoin "Tony" Rezko, onetime Blagojevich fundraiser and insider, also recently started providing prosecutors with detailed information about his alleged role in the scheme, sources have said. Kelly and Rezko were long viewed as a one-two punch in Blagojevich's efforts to raise millions of dollars in campaign contributions.

Kelly's testimony would be valuable to prosecutors. In addition to knowing the ins-and-outs of the Blagojevich money machine, Kelly has long been one of the former governor's closest friends. He and Rezko allegedly were given great influence in the administration to award state business and name people to state boards and commissions as they sought to raise campaign contributions.